This invention relates to a method of making a hydrophilic carbon fiber construction by immersing a carbon fiber construction in an aqueous dispersion of a metal oxide comprising: i) 1-15% by weight metal oxide and ii) 0.01%-5% by weight dispersant; followed by heating the carbon fiber construction to remove the dispersant.
U.S. Pat. No. 5,840,414 discloses a carbon plate for use in a fuel cell system which is rendered hydrophilic by incorporation of a metal oxide. The reference lists potential methods at col. 5, lines 31-52. The reference describes in detail and exemplifies a three-step method of incorporating metal oxide in a graphite plate by treatment with a metal chloride, in situ conversion of the metal chloride to metal hydroxide, and in situ conversion of the metal hydroxide to metal oxide. (col 5, line 53-col. 6, line 21; and col. 7, lines 7-25).
U.S. Pat. No. 5,998,058 discloses an electrode backing layer for a polymer electrolyte membrane fuel cell formed from a carbon fiber substrate treated so as to contain both xe2x80x9chydrophilicxe2x80x9d and xe2x80x9chydrophobicxe2x80x9d pores. The reference describes a method of making pores more hydrophilic by immersion in a solution of tin tetrachloride pentahydrate followed by immersion in ammonia.
U.S. Pat. No. 6,024,848 discloses a porous support plate for an electrochemical cell which includes a contact bilayer adjacent to an electrode including a hydrophobic and a hydrophilic phase. The reference discloses a hydrophilic phase comprised of a mixture of carbon black and a proton exchange resin.
Briefly, the present invention provides a method of making a hydrophilic carbon fiber construction comprising the steps of: a) immersing a carbon fiber construction in an aqueous dispersion of one or more metal oxides, comprising: i) 1-15% by weight metal oxide; ii) 0.01%-5% by weight dispersant; and b) subsequently heating the carbon fiber construction sufficiently to remove substantially all of the dispersant. Typically the aqueous dispersion contains 1-5% by weight metal oxide, more typically 1-3% by weight metal oxide and more typically 1.5-2.5% by weight metal oxide. Typically the metal oxide is selected from oxides of Sn, Si, Zr, Ti, Al, and Ce, most typically SnO2. Typically the dispersant is a non-ionic dispersant such as an alcohol alkoxylate such as Triton(trademark) X100. Typically the immersion step can be completed in less than 30 minutes, more typically in less than 10 minutes, and most typically in less than 1 minute. Typically the entire method can be completed in less than 30 minutes, more typically in less than 20 minutes, most typically in less than 5 minutes.
In another aspect, the present invention provides a hydrophilic carbon fiber construction made according to the method of the present invention, typically having a loading of metal oxide equivalent to 20-50 mg metal per gram of carbon.
What has not been described in the art, and is provided by the present invention, is a simple and speedy method of making a hydrophilic carbon fiber construction impregnated with a uniform coating of a metal oxide.
In this application the terms xe2x80x9csurfactantxe2x80x9d and xe2x80x9cdispersantxe2x80x9d are used interchangeably.
It is an advantage of the present invention to provide a simple and speedy method, typically taking approximately 15 minutes, for making a hydrophilic carbon fiber construction impregnated with a uniform coating of a metal oxide, which is useful as an electrode backing layer or gas diffusion layer in an electrolytic cell such as a fuel cell. It is an advantage of the present invention that it requires no vacuum source to wet out the treated substrate. It is an advantage of the present invention that it requires only a single liquid immersion tank. It is an advantage of the present invention that it requires no monitoring or addition of chemicals during treatment. It is an advantage of the present invention that it avoids the use of chemicals as toxic and corrosive as tin tetrachloride pentahydrate, used in some prior art processes.